The present invention relates to light sensitive photochromic contact lenses and methods for manufacturing. More particularly, the invention relates to contact lenses having light sensitive substances such as photochromic materials located within the central portion or pupillary region of the lens. The methods for manufacturing are applicable, in one non-limiting embodiment, to the cast molding method of producing contact lenses.
Photochromism is a phenomenon involving a light induced reversible change in color. An article containing such a material that becomes colored upon exposure to light radiation containing ultraviolet rays will revert to the original color when the influence of the ultraviolet radiation is discontinued. Sources of light radiation that contain ultraviolet rays include, for example, sunlight and the light of a mercury lamp. Discontinuation of the ultraviolet radiation can be achieved for example by storing the photochromic material or article in the dark or by removing the source of ultraviolet radiation (e.g., by means of filtering).
Photochromic contact lenses pose a unique set of challenges. The surface of the eye is a challenging environment for contact lenses containing photochromic molecules that typically experience diminished performance at temperatures above 70° F. (21° C.). The contact lens material, typically composed of 50% or more of water, is marginally compatible with what are typically very highly lypophilic molecules. Also, the eye is strongly shaded from the ultraviolet light required for activation of photochromic molecules by the brow and eyelashes.
Although methods for incorporating photochromic materials into contact lenses have been disclosed, a need remains for a fast reliable method of manufacturing photochromic contact lenses wherein the light sensitive substance is located within the central portion or pupillary region of the lens. Moreover there is a need for this process to be economical and readily adaptable to very automated equipment used today to manufacture contact lenses, e.g., hydrophilic cross-linked contact lenses.